Steps to repro:
1) Get a machine that does NOT have Team Explorer or Visual Studio installed
2) Install Test Studio
3) Use our UI to try to connect to TFS on the cloud

Expected: you get an error message explaining that we use DLLs that are part of Team Explorer and you need to install either Team Explorer, which is free, or Visual Studio.
Actuall: you get an error message that says "Source control plugin was not found". If you look at the application log you can see a FileNotFound exception for Microsoft.TeamFoundation.Client.